Cosmology: The Professor’s Old Clothes

Posted in Education, The Universe and Stuff with tags , , , , , , , on January 19, 2018 by telescoper

After spending  a big chunk of yesterday afternoon chatting the cosmic microwave background, yesterday evening I remembered a time when I was trying to explain some of the related concepts to an audience of undergraduate students. As a lecturer you find from time to time that various analogies come to mind that you think will help students understand the physical concepts underpinning what’s going on, and that you hope will complement the way they are developed in a more mathematical language. Sometimes these seem to work well during the lecture, but only afterwards do you find out they didn’t really serve their intended purpose. Sadly it also  sometimes turns out that they can also confuse rather than enlighten…

For instance, the two key ideas behind the production of the cosmic microwave background are recombination and the consequent decoupling of matter and radiation. In the early stages of the Big Bang there was a hot plasma consisting mainly of protons and electrons in an intense radiation field. Since it  was extremely hot back then  the plasma was more-or-less  fully ionized, which is to say that the equilibrium for the formation of neutral hydrogen atoms via

p+e^{-} \rightarrow H+ \gamma

lay firmly to the left hand side. The free electrons scatter radiation very efficiently via Compton  scattering

\gamma +e^{-} \rightarrow \gamma + e^{-}

thus establishing thermal equilibrium between the matter and the radiation field. In effect, the plasma is opaque so that the radiation field acquires an accurate black-body spectrum (as observed). As long as the rate of collisions between electrons and photons remains large the radiation temperature adjusts to that of the matter and equilibrium is preserved because matter and radiation are in good thermal contact.

 

Image credit: James N. Imamura of University of Oregon.

Eventually, however, the temperature falls to a point at which electrons begin to bind with protons to form hydrogen atoms. When this happens the efficiency of scattering falls dramatically and as a consequence the matter and radiation temperatures are no longer coupled together, i.e. decoupling occurs; collisions can longer keep everything in thermal equilibrium. The matter in the Universe then becomes transparent, and the radiation field propagates freely as a kind of relic of the time that it was last in thermal equilibrium. We see that radiation now, heavily redshifted, as the cosmic microwave background.

So far, so good, but I’ve always thought that everyday analogies are useful to explain physics like this so I thought of the following.

When people are young and energetic, they interact very extensively with everyone around them and that process allows them to keep in touch with all the latest trends in clothing, music, books, and so on. As you get older you don’t get about so much , and may even get married (which is just like recombination, not only that it involves the joining together of previously independent entities, but also in the sense that it dramatically  reduces their cross-section for interaction with the outside world).  As time goes on changing trends begin to pass you buy and eventually you become a relic, surrounded by records and books you acquired in the past when you were less introverted, and wearing clothes that went out of fashion years ago.

I’ve used this analogy in the past and students generally find it quite amusing even if it has modest explanatory value. I wasn’t best pleased, however, when a few years ago I set an examination question which asked the students to explain the processes of recombination and decoupling. One answer said

Decoupling explains the state of Prof. Coles’s clothes.

Anyhow, I’m sure there’s more than one reader out there who has had a similar experience with an analogy that wasn’t perhaps as instructive as hoped or which came back to bite you. Feel free to share through the comments box…

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Hair from Bayeux

Posted in Beards, History with tags , , , , on January 18, 2018 by telescoper

Since the Bayeux Tapestry (which, being stitched rather than woven, is an embroidery rather than a tapestry) is in the news I thought I’d share some important information about the insight this article gives us into 11th century hairstyles.

As you know the Bayeux Tapestry Embroidery concerns the events leading up to the Battle of Hastings between the Saxons (who originated in what is now a part of Germany) led by Harold Godwinson (who had relatives from Denmark and Sweden) and the Normans (who lived at the time in what is now France, but who came originally from Scandinavia).

Most chronicles of this episode leave out the important matter of the hair of the protagonists, and I feel that it is important to correct this imbalance here.

Throughout the Bayeux Untapestry, the Saxons are shown with splendid handlebar moustaches, exemplified by Harold Godwinson himself:

This style of facial hair was obviously de rigueur among Saxons. The Normans on the other hand appeared to be clean-shaven, not only on their front of their heads but also on the back:

This style of coiffure looks like it must have been somewhat difficult to maintain, but during the Battle of Hastings would mostly have been hidden under helmets.

With a decisive advantage in facial hair one wonders how the Saxons managed to lose the battle, but I can’t help thinking the outcome would have been different had they had proper beards.

Beyond Falsifiability: Normal Science in a Multiverse

Posted in The Universe and Stuff with tags , , , , , , on January 17, 2018 by telescoper

There’s a new paper on the arXiv by Sean Carroll called Beyond Falsifiability: Normal Science in a Multiverse. The abstract is:

Cosmological models that invoke a multiverse – a collection of unobservable regions of space where conditions are very different from the region around us – are controversial, on the grounds that unobservable phenomena shouldn’t play a crucial role in legitimate scientific theories. I argue that the way we evaluate multiverse models is precisely the same as the way we evaluate any other models, on the basis of abduction, Bayesian inference, and empirical success. There is no scientifically respectable way to do cosmology without taking into account different possibilities for what the universe might be like outside our horizon. Multiverse theories are utterly conventionally scientific, even if evaluating them can be difficult in practice.

I’ve added a link to `abduction’ lest you think it has something to do with aliens!

I haven’t had time to read all of it yet, but thought I’d share it here because it concerns a topic that surfaces on this blog from time to time. I’m not a fan the multiverse because (in my opinion) most of the arguments trotted out in its favour are based on very muddled thinking. On the other hand, I’ve never taken seriously any of the numerous critiques of the multiverse idea based on the Popperian criterion of falsifiability because (again, in my opinion) that falsifiability has very little to do with the way science operates.

Anyway, Sean’s papers are always interesting to read so do have a look if this topic interests you. And feel free to comment through the box below.

Cyrille Regis and Racism in Football

Posted in Football with tags , on January 16, 2018 by telescoper

Cyrille Regis, shown here playing for Coventry City in the 1987 FA Cup against Tottenham Hotspur

 

On my way to the airport yesterday I heard the sad news of the death, at the age of just 59, of the footballer Cyrille Regis.  I’ll leave it to those more qualified to post full obituaries of the man – I couldn’t possibly do justice to him as a player and a person – and will confine myself to one memory that remains strong in my mind.

While I was a student at Cambridge there was a University branch of the Newcastle United Supporters Club. This was mainly for social gatherings but, during term time, and when the game was within reach of a day trip we hired a coach or minibus and went to Newcastle United’s away games. Our team had just been promoted to the old First Division at the end of the 1983/4 season and we all wanted to see as much as possible of them in the top flight.

And so it came to pass that on 13th October 1984 we went by coach to Highfield Road to see Coventry City versus Newcastle United. It wasn’t a great game. In fact, it had been picked as the featured match on Match of the Day that Saturday night. When we got back to Cambridge and settled in the JCR to watch it we heard Jimmy Hill (who presented the show in those days) that they were joining the action mid-way through the second half. The first half had not been deemed worthy of transmission.

Despite the generally low quality of the game, there was one star who was easily the best player on the field and  that was Cyrille Regis, who even eclipsed the little magician Peter Beardsley, whom the away fans had come to watch. Powerfully built, with a good turn of speed and excellent in the air despite not being particularly tall, Cyrille Regis proved a constant handful for Newcastle’s central defenders, winning just about every contested header and beating them for pace seemingly at will. In the second half Glen Roeder stopped even bothering to challenge for the ball in the air as he knew Regis had the beating of him.  Newcastle, however, played five at the back for away games in those days and they managed to stop him scoring.

The game ended 1-1 with  Peter Beardsley scoring for Newcastle from the penalty spot in front of the away supporters for Newcastle and Kenny Hibbitt scoring for Coventry. Here are some of the highlights of the game:

An away draw in the First Division was an acceptable result but, unhappily, the memories I have of the match are blighted by what I recall of the actions of some of the Newcastle United supporters who shouted racist abuse and threw bananas onto the pitch whenever Regis came within range. Their behaviour was disgraceful. In mitigation there were only a few – probably a couple of dozen among 4000-odd travelling suporters  doing this – and many of the rest of us shouted at them to shut the f**k up. But the fact that there were any at all is bad enough. It ruined the day for me, and left me feeling deeply ashamed, but as far as I could tell Cyrille Regis just ignored it; this sort of thing probably happened every time he played. How he managed to keep his composure I’ll never know.

Those of us who have never experienced racist abuse can’t really imagine what it must be like to be on the receiving end. The dignity of men like Cyrille Regis in the face of this sort of thing speaks volumes about his strength of character. Above all, he tried to silence the racists by concentrating on his game and being an outstanding player.

All this was over thirty years ago and we like to think that racism is nowadays far less of an issue in football.  I rarely go to live games now, so I can’t really comment on how crowd behaviour has or hasn’t changed. However, judging by the comments of black players racism is still endemic, it’s just that most of the racists refrain from some of the more overt displays of obnoxious behaviour – such as throwing bananas – because they would (rightly) get the perpetrators ejected from the ground. Dealing with the symptoms, however, doesn’t cure the disease.

It seems that even Peter Beardsley (who played in the match I mentioned above and is now, at 54, Newcastle United’s Under-23 coach) has been accused by young players of bullying and racist comments. He denies the allegations, and is on leave while the charges are investigated. I’m not going to prejudge what the outcome of those investigations will be, but his case is a reminder – as if we needed it – that racism hasn’t gone away.

 

 

The WNO Orchestra at St David’s Hall

Posted in Music with tags , , , , , on January 15, 2018 by telescoper

It has been a very busy weekend but yesterday afternoon I took time out to visit St David’s Hall in Cardiff to hear the Orchestra of Welsh National Opera conducted by Tomáš Hanus in a programme of music by Beethoven, Mendelssohn and Dvořák. I’ve noticed that many of the international concerts that are a regular part of Cardiff life have been moved from weekday evenings to weekend afternoons. No doubt that it is for commercial reasons. I have to admit that I’m not a big fan of matinee concerts, but as it happens I’m not going to be available for many of the weekday evening concerts for the foreseeable future so I thought I’d give this one a go. The programme was a middle-of-the-road bums-on-seats affair, but if it brings people into the concert hall that is a good thing and it was nice to see a big crowd, including a sizeable contingent of schoolchildren, there to enjoy the show.

First up we had a favourite piece of mine, Beethoven’s  Egmont overture, inspired by the story of Lamoral, Count of Egmont whose execution in 1568 sparked an uprising Spanish occupation that eventually led to the independence of the Netherlands. It’s a stirring, dramatic work, ideal for opening a concert programme. I thought the tempo was a bit slow at the start, which made increase in speed towards the end a little jarring, but otherwise it was well played the full orchestra, arranged with six double-basses right at the back of the stage facing the conductor with the brass either side. That was very effective at generating a rich dark sonority both in this piece and in the Dvořák later on.

The next item was a very familiar work indeed, the Violin Concerto in E minor by Felix Mendelssohn. This is perhaps best known for its lvoely second movement (in which they key changes to C major) but the other two movements are really innovative and virtuosic. In the wrong hands the slow movement can be horribly schmaltzy but Norwegian soloist Henning Kraggerud managed to bring out is beauty without wallowing in its romanticism. It was a very fine performance, warmly appreciated by the audience. Henning Kraggerud treated us to an encore in the form of an intruguing piece by a musician previously unknown to me, Olof Bull, a fellow Norwegian and a contemporary of Mendelssohn.

After the wine break the main event of was another familiar piece, the Symphony No. 9 (“From the New World”) by Antonín Dvořák, a piece full of nostalgia for his Czech homeland written while the composer was living in America. It’s a piece I’ve heard very many times but it still manages to stay fresh, and yesterday’s performance was full of colour of verve. Tomáš Hanus (himself Czech) chose this piece as a tribute to an old friend who passed away last year, and it was was played with great passion.

I’d heard all the pieces in this programme many times, both in concert and on record, but they all stand up to repeated listening, simply because they’re so very good. I do like to hear new works – and do wish the programming at St David’s Hall were a little more adventurous – but they do have to make ends meet and there’s in any case much to enjoy in the standard repertoire, especially when it’s played by a fine orchestra. Such pieces can fall flat when you get the feeling that the musicians themselves are a bit bored with them, but that emphatically wasn’t the case yesterday.

It will soon be time to Welsh National Opera’s new season, with a new production of Verdi’s La Forza del Destino alongside revivals of Tosca and Don Giovanni. It’s going to be tricky to see them all, but I’ll give it a go!

The Crossword Puzzle Sketch

Posted in Crosswords with tags , , on January 13, 2018 by telescoper

Fifty years old, and starring the wonderful Beryl Reid, here’s a classic sketch about (of all things) … crosswords!

Yellow Tango

Posted in Jazz with tags , , , on January 12, 2018 by telescoper

Before Christmas I posted one of my favourite pieces of music, The Fable of Mabel, performed by a band led by Serge Chaloff and featuring pianist Dick Twardzik (who also composed the piece). I thought I’d follow this up with another piece by Twardzik, this time in a trio with Carson Smith on bass and the excellent Peter Littman on drums.

This piece was recorded in late 1954, at which time the two great influences on jazz piano were Bud Powell and Thelonious Monk. Here’s a good example of how Twardzik manages to nod in the very different directions of these two great musicians – the Monk influence in particular stands out a mile when the rhythm switches from Latin-American to 4/4 at about 1:43 – while also managing to find a very original voicea which was all his own. It’s such a terrible shame that within a few months of this session Twardzik was dead (of a heroin overdose, at the age of 24) and jazz had lost one of its most promising young artists.